Currently, with the vigorous development of the broadband wireless access techniques, the technique of using the wireless resources to implement the broadband metropolitan access presents great vitality and has unanticipated potential markets.
Meanwhile, the radio frequency spectrum resources are fairly precious. Especially at an area that is not well planned or does not have licensed frequency bands, a plurality of base stations (BSs) may operate within the same channel. As a result, systems where the plurality of BSs belongs to are interfered with each other. In order to coordinate the coexistence among different devices under the same frequency band, especially the coexistence among devices under a License-Exempt (LE) frequency band, certain coexistence mechanisms among devices need to be constructed.
A neighboring BS mentioned in the present invention refers to a BS with a valid common coverage area, that is, a BS containing valid subscriber stations (SSs) in the common coverage area. For example, as shown in FIG. 1, a BS1 and a BS2 are located quite close to each other in terms of geography positions, and any one of the BS1 and the BS2 is located within the other's coverage area; however, since there are no SSs within the common coverage area of the BS1 and the BS2, no severe influences are caused to the wireless networks of each other, and thus the BS1 and the BS2 are not neighboring BSs. An overlapping area between the BS2 and a BS3 is smaller, and neither the BS2 nor the BS3 is located within the other's coverage area; however, there are SSs within the overlapping area there-between, which may cause interferences to the wireless networks of each other, so the BS2 and the BS3 are neighboring BSs herein.
A community mentioned herein refers to a set of a group of BSs under the same environment, in which any sub-set formed by one BS or some BSs at least has a valid common coverage area with a BS within the community that does not belong to the sub-set.
Due to the above-mentioned potential competition about resources, it is quite important for the BSs under the LE frequency band to negotiate with neighboring BSs to solve the coexistence problem. When distributing air interface resources, the BS utilizes competitive air interface resources (for example, a time period, a sub-channel, and the like) to make communications with SSs in non-interferential areas, and utilizes exclusive air interface resources (for example, a time period, a sub-channel, and the like) to make communications with SSs in interferential areas.
In the LE frequency band, there may be interferences caused by different types of BSs. In order to enable negotiations among different types of BSs, certain intervals need to be divided between frames under normal communication, so as to transmit energy signals and to bear a coexistence signaling. Such intervals are called coexistence signaling intervals (CSIs) herein. The CSI presents according to a certain cycle, and the parameters of the CSI, such as an initial position and an interval length, must be stipulated and known by all the BSs in the LE frequency band within each community of the same area.
Within a community, each BS periodically broadcasts a coexistence signaling message thereof in the CSI interval, and an initializing BS (IBS) also needs to broadcast a coexistence signaling message thereof, so as to enable a negotiation with neighboring BSs. The coexistence signaling message includes a BS address, a proxy server address, or a BS identifier (BSID), and is completely transmitted within one frame formed by one or more CSI intervals.
Operating BSs (OBSs) broadcast coexistence signaling messages thereof according to the same cycle within the same community. The BSs occupying different resources may share the same CSI. For example, as shown in FIG. 2, one community includes N channels, 16 CSIs are taken as one circulating cycle, so that each BS selects to occupy one CSI from the 16 CSIs, and the BSs on the same channel cannot share the same CSI. It is assumed that 10 CSIs are required for completely transmitting a coexistence signaling message of a BS, 160 CSIs are required for completely broadcasting one coexistence signaling message of the BS.
In a CSI interval, the BS broadcasts the message in a form of energy symbols, that is, information about 0, information about 1, starting information, or finishing information is respectively represented by an energy magnitude of a sent signal. As shown in FIG. 3, each energy symbol includes two parts, namely Part 1 and Part 2. As for the symbol 0, both Part 1 and Part 2 do not have sending energy; as for the symbol 1, both Part 1 and Part 2 have the same sending energy at a certain quality; and as for the starting and finishing symbols, only one of Part 1 and Part 2 has a certain sending energy. During a receiving motion, if the energies of Part 1 and Part 2 are both lower than a preset threshold, it is determined that the transmitted symbol is 0, and if the energies of Part 1 and Part 2 are both higher than the preset threshold, it is determined that the transmitted symbol is 1. Especially, if the energy of Part 1 is different from that of Part 2, it may be determined as a starting symbol or a finishing symbol. One CSI interval is able to deliver one or more energy symbols.
The above mechanism can solve the problem about communication resource negotiation when an IBS in the LE frequency band joins a community, but cannot solve the following problems.
As shown in FIG. 4, when a subscriber station 1 (SS1) is located at an original position indicated by a dashed line, the BS3 and the BS4 do not have valid common coverage area with each other, so they are not neighboring BSs. However, when the SS1 moves from the position indicated by the dashed line to a position indicated by a solid line, the BS3 and the BS4 are turned to become neighboring BSs, and accordingly, the community where the BS3 belongs to and the community where the BS4 belongs to need to be converged, so that the BS3 may bring co-channel interference (CCI) to the SS1. Definitely, other factors such as changes in environmental conditions may also cause two BSs that originally are not neighboring BSs to become neighboring BSs.
If the BS3 and the BS4 originally occupy the same resources, the two BSs may cause interferences at the SS1, so that the two BSs need to negotiate with each other about the communication resources, thereby realizing a coexistence effect. Assuming that the BS3 and the BS4 just occupy the same CSI, the SS1 fails to recognize an energy message broadcasted by the BS3 in the CSI, that is, fails to recognize the interferences, and thus the BS3 and the BS4 fail to enable a negotiation.
To sum up, if two OBSs originally are not neighboring BSs, they definitely can share the same CSI channel. Unfortunately, if the two OBSs are turned into neighboring BSs due to certain reasons such as environmental change or movement of SS, the SS under interferences cannot detect the newly appeared OBS neighboring BS.
Therefore, a mechanism for ensuring that the SS can detect the interference and identify an interferential source is needed, so as to achieve a coexistence mechanism for making negotiations among BSs.
In the above example, due to the SS1, the two OBSs are turned to become neighboring BSs. Since the two OBSs work in the same channel, the SS1 fails to correctly receive information about the BS thereof, but the SS1 can simulate a neighboring BS to produce interferences by using the known CSI information, and then broadcast the interferences to the surrounding SSs. The known CSI information includes a position or a cycle and a CSI reserved for the IBS, and the like. Accordingly, the SS1 simulates a neighboring BS to produce interferences in the CSI cycle reserved for the IBS, and broadcasts the interferences to the surrounding SSs. Such technique requires additional SSs existing surrounding the SS1, otherwise it cannot be used.
Therefore, a technical solution for detecting neighboring BS interference by an SS is needed, so as to solve the problems in the above prior art.